Manufacturers look at diesels for U.S.

With gas prices near historic highs in the U.S., many people are feeling the pinch. That's especially true as we head into the vacation season, when most Americans do most of their driving.

The prospect of pricey fill-ups threatens to turn this into the summer of our discontent. High gas prices hit hardest the vehicles that are least fuel efficient. That description applies to two of the most popular forms of transportation in this country - pickup trucks and sport-utility vehicles.

The question becomes, how do we keep driving what we want to, without driving ourselves broke? One of the options presented in recent years is hybrids - gas and electric powered vehicles. This combined power source technology was first found in small cars and is slowly making its way into smaller SUVs. Another possible solution is one that has long been practiced in Europe - and long ignored here in the states. That option is diesel power.

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For many people, the mention of "diesel" conjures up images of smoky, smelly tractor-trailers, rolling down the interstate. But, the science is advancing rapidly in this field and diesel engines these days are cleaner and more efficient than they were in the past. As a result, several manufacturers are looking at the U.S. market to see if the time is right to reconsider diesel.

Count BMW among the manufacturers who are assessing the situation in the states. Recently, they made available a European sport-utility vehicle for evaluation by the American automotive press. The model is the 2004 X5 - BMW's largest SUV. While diesel is new to most Americans, it's not new to BMW. They have been manufacturing diesel motors for over 20 years and some 45 percent of the company's products in Europe are diesel-powered. The X5 version is offered with two diesel motors. (BMW X5 3.0d is not sold in U.S.)

I drove the 3.0d - a 3.0-liter inline six-cylinder engine, coupled to a five-speed automatic transmission. The turbocharged 3.0d uses common rail direct injection for fuel delivery. Key to the system is its high injection pressure. High pressure makes for a finer fuel spray, which in turn leads to more efficient fuel combustion. Better combustion yields more power, increased fuel economy and less noise.

The 3.0d produces 184 horsepower at 4,000 rpm and 302 lbs.-ft. of torque between 2,000 and 3,000 rpm. The impressive torque numbers, peaking low in the engine's rev range, means that the X5 diesel pulls quickly and easily off the line. Abundant torque also aids in towing, though all X5 models are rated with the same maximum capacity (6,000 pounds).

Idle on diesel engines is traditionally rougher and noisier than gas engines, but the 3.0d shows little of either characteristic. The X5 diesel achieves more torque and less horsepower than the base, gas motor available in the U.S. (the 3.0i). On paper, that suggests more low-end pull for the diesel, more high-end speed for the gasser. On pavement, the paper is proven correct. The 3.0d rolls easily from a stop and moves smoothly in the lower registers.

The U.S.-spec 3.0-liter six-cylinder is noticeably quicker in the upper registers than the diesel, and passing is easier in the gas-powered X5 - except as it relates to passing gas stations. The U.S. gasoline-powered X5 rates 16 miles per gallon in the city, 21 mpg highway. The diesel averages about 30 percent better in fuel economy.

That translates into fewer fueling stops. The bottom line on drivability is that the diesel feels strongest at low speeds, weakest in flat-out acceleration drills, and no different at all when cruising down the road at highway speeds.

Engine choice aside, the X5's capabilities and capacities are virtually the same. These are full-time, all-wheel-drive vehicles that ride easily and comfortably on-road, and tackle light off-road as well. The interior is well appointed, seats five and there's a generous cargo hold in back.

The less different it feels from what we're used to, the more likely we Americans are to accept new technology. The best modern diesel engines offer the driver an experience that's close to what he or she would have in a gas-powered vehicle. If BMW can vault the hurdles of shifting emissions regulations and bring the X5 diesel to market here, consumers would have another option for having their cake and eating it too - in this case, keeping their SUVs without losing their shirts on fuel costs.